Active noise cancellation (ANC) is a technique that aims to “cancel” unwanted noise, by introducing an additional, electronically controlled sound field that is also referred to as anti-noise. This technique helps make playback from a media player, or a downlink communications signal in a telephony device, to sound better, or be more intelligible to the listening user. An ANC sub-system may be implemented in a variety of different personal consumer electronic devices such as smartphones, headsets (including wireless headsets), and tablet computers, which are used in environments that are sometimes quiet and sometimes noisy. The anti-noise is electronically manipulated or adjusted to have the proper pressure, amplitude and phase so as to destructively interfere with the ambient or background noise that makes it into the user's ear canal. A residual noise or error remains, which can be picked up by an error sensor, typically an error microphone that is located just in front of the earpiece speaker driver from which the anti-noise is produced.
The use of ANC is expected to be primarily limited to environments that are sufficiently loud, loud enough that the background noise could potentially obstruct the quality or intelligibility of the user content (e.g., music or speech) that is being heard by the user. As such, in environments in which the ambient or background noise is not so loud, ANC may not add significant value and as such it may be turned off. This will help preserve battery life in a portable device, since in many instances the acoustic environment surrounding the user of the portable device is not hostile, i.e. it is relatively quiet, such that running an ANC process provides insignificant user benefits.